What Is Metformin?

Metformin is an oral medication that has been used to treat Type 2 diabetes for decades. It belongs to a class of drugs called biguanides and remains the first-line medication recommended by most major diabetes organisations worldwide — including the American Diabetes Association (ADA) and Diabetes UK — for people with Type 2 diabetes who need medication beyond lifestyle changes.

It is available in standard and extended-release forms, usually taken once or twice daily with meals.

How Does Metformin Work?

Unlike some diabetes medications that stimulate the pancreas to produce more insulin, metformin works primarily by reducing the amount of glucose the liver releases into the bloodstream. It also helps the body's cells respond more effectively to insulin (improving insulin sensitivity) and slightly slows glucose absorption from food.

In practical terms: it addresses the root mechanisms of Type 2 diabetes rather than simply forcing more insulin production.

Key Benefits

  • Effective blood sugar control: Metformin reliably lowers HbA1c levels, often by 1–2 percentage points.
  • Weight neutral or modest weight loss: Unlike some diabetes medications that cause weight gain, metformin tends to be weight neutral and may support modest weight reduction.
  • Low hypoglycaemia risk: Because it doesn't trigger extra insulin release, metformin alone rarely causes dangerous low blood sugar episodes.
  • Cardiovascular benefits: Long-term data suggest metformin may offer protective effects on the heart and blood vessels, which is particularly relevant given diabetes's cardiovascular risks.
  • Affordable and widely available: As a generic medication, metformin is one of the most cost-accessible diabetes treatments available.

Common Side Effects

The most frequently reported side effects are gastrointestinal — nausea, diarrhoea, stomach cramps, and a metallic taste. These are most common when starting treatment or increasing the dose. Strategies to manage them include:

  • Always taking metformin with food.
  • Starting at a low dose and increasing gradually.
  • Switching to the extended-release version, which many people tolerate better.

For most people, GI side effects improve significantly after the first few weeks.

Important Considerations and Cautions

  • Vitamin B12 levels: Long-term metformin use can reduce B12 absorption. Your doctor may recommend periodic B12 monitoring and supplementation if needed.
  • Kidney function: Metformin is processed through the kidneys and requires dose adjustment or discontinuation in people with significantly reduced kidney function. Regular kidney function checks are standard practice.
  • Contrast dye procedures: Metformin is typically paused around certain medical imaging procedures that use contrast dye. Always inform your medical team that you take it.
  • Alcohol: Drinking heavily while taking metformin raises the rare risk of lactic acidosis. Moderate alcohol consumption is generally considered acceptable, but discuss this with your doctor.

Who Might Not Be Suitable for Metformin?

While metformin is suitable for most people with Type 2 diabetes, it may not be appropriate for those with:

  • Significantly impaired kidney function (below a certain eGFR threshold)
  • Severe liver disease
  • A history of lactic acidosis

If metformin isn't suitable, there are several other medication classes — including SGLT2 inhibitors, GLP-1 receptor agonists, and DPP-4 inhibitors — that your doctor can consider.

A Note on Medication and Lifestyle

Metformin works best as part of a broader management plan. It's not a substitute for healthy eating, regular exercise, and other lifestyle factors — but for many people, it's a valuable and well-tolerated addition to that foundation. If you have questions about whether metformin is right for you, or about how it interacts with other medications, always speak directly with your prescribing doctor or pharmacist.